fix(frame-title): ignore frames with negative tabindex

lib/rules/frame-title.json

@@ -1,6 +1,7 @@
 {
   "id": "frame-title",
   "selector": "frame, iframe",
+  "matches": "no-negative-tabindex-matches",
   "tags": [
     "cat.text-alternatives",
     "wcag2a",

lib/rules/no-negative-tabindex-matches.js

@@ -0,0 +1,6 @@
+function noNegativeTabindexMatches(node, virtualNode) {
+  const tabindex = parseInt(virtualNode.attr('tabindex'), 10);
+  return isNaN(tabindex) || tabindex >= 0;
+}
+
+export default noNegativeTabindexMatches;

test/integration/rules/frame-title/frame-title.html

@@ -64,3 +64,8 @@
   role="presentation"
   tabindex="0"
 ></iframe>
+<iframe
+  src="/integration/rules/frame-title/frames/level1a.html"
+  id="inapplicable1"
+  tabindex="-1"
+></iframe>

test/rule-matches/no-negative-tabindex.js

@@ -0,0 +1,41 @@
+describe('no-negative-tabindex-matches', function() {
+  'use strict';
+
+  var fixture = document.getElementById('fixture');
+  var queryFixture = axe.testUtils.queryFixture;
+  var rule = axe.utils.getRule('frame-title');
+
+  afterEach(function() {
+    fixture.innerHTML = '';
+  });
+
+  it('returns true for nodes with no tabindex', function() {
+    var vNode = queryFixture('<div id="target"></div>');
+    var actual = rule.matches(null, vNode);
+    assert.isTrue(actual);
+  });
+
+  it('returns true for nodes with a zero tabindex', function() {
+    var vNode = queryFixture('<div id="target" tabindex="0"></div>');
+    var actual = rule.matches(null, vNode);
+    assert.isTrue(actual);
+  });
+
+  it('returns true for nodes with a positive tabindex', function() {
+    var vNode = queryFixture('<div id="target" tabindex="4"></div>');
+    var actual = rule.matches(null, vNode);
+    assert.isTrue(actual);
+  });
+
+  it('returns true for nodes with an invalid tabindex', function() {
+    var vNode = queryFixture('<div id="target" tabindex="foo"></div>');
+    var actual = rule.matches(null, vNode);
+    assert.isTrue(actual);
+  });
+
+  it('returns false for nodes with an invalid tabindex', function() {
+    var vNode = queryFixture('<div id="target" tabindex="-10"></div>');
+    var actual = rule.matches(null, vNode);
+    assert.isFalse(actual);
+  });
+});